Load PNG and read pixels in PHP without GD?

Question

I have a need to read in the exact unaltered pixel data (ARGB) from a truecolour PNG file, preferably from PHP.

Unfortunately the GD library in PHP messes with the alpha channel (reducing it from 8-bit to 7-bit), making it unusable.

I'm currently assuming that my options are either:

1. Implement my own raw PNG reader to extract the necessary data.
2. Use some less-broken language/library and call it from the PHP as a shell process or CGI.

I'd be interested to hear any other ideas, though, or recommendations for one way over the other...

: I think #1 is out.：我认为＃1已经出局了。 I've tried passing the IDAT data stream to gzinflate(), but it just gives me a data error. (Doing the exact same thing, with the exact same data, outside of PHP produces the expected result.)

Answer 1

How about ImageMagick?

<?php
$im = new Imagick("foo.png");
$it = $im->getPixelIterator();

foreach($it as $row => $pixels) {
    foreach ($pixels as $column => $pixel) {
        // Do something with $pixel
    }

    $it->syncIterator();
}
?>

Answer 2

You can use the pngtopnm function of netpbm to convert the PNG to an easily parsed PNM. Here is a somewhat naive php script that should help you get what you need:

<?php
$pngFilePath = 'template.png';
// Get the raw results of the png to pnm conversion
$contents = shell_exec("pngtopnm $pngFilePath");
// Break the raw results into lines
//  0: P6
//  1: <WIDTH> <HEIGHT>
//  2: 255
//  3: <BINARY RGB DATA>
$lines = preg_split('/\n/', $contents);

// Ensure that there are exactly 4 lines of data
if(count($lines) != 4)
    die("Unexpected results from pngtopnm.");

// Check that the first line is correct
$type = $lines[0];
if($type != 'P6')
    die("Unexpected pnm file header.");

// Get the width and height (in an array)
$dimensions = preg_split('/ /', $lines[1]);

// Get the data and convert it to an array of RGB bytes
$data = $lines[3];
$bytes = unpack('C*', $data);

print_r($bytes);
?>